Canon EF 17-40mm f/4 USM L - Retest @ 15mp - Analysis
Lens Reviews - Canon EOS (APS-C)
Article Index
Introduction
Analysis

Distortion

The lens produces a quite strong degree of barrel distortion at 17mm (~2.5%). At 24mm there is very slight barrel distortion whereas at 40mm the problem is negligible. Compared to native APS-C lenses this is fairly moderate.

The charts below show the findings based on the initial test - the distortion characteristic cannot change just by mounting the lens to a different (APS-C) DSLR.

Move the mouse cursor over the focal length text marks below to observe the respective distortion
17mm 24mm 40mm

Vignetting

APS-C DSLRs such as the EOS 50D can take advantage of the sweet spot of full format lenses so vignetting is no big issue with the 17-40mm f/4L. It's basically possible to use the max. aperture without disturbing edge shading.

MTF (resolution)

The EF 17-40mm f/4 L showed a very good performance in the lab. The center quality is on a very good to excellent level throughout the tested range. The borders are generally very sharp as well although it helps to stop down a little (f/5.6) - same goes for the extreme corner performance. The peak quality is reached between f/5.6 and f/8. Thereafter diffraction effects introduce a negative effect (unavoidable).

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

Chromatic aberrations (color shadows at harsh contrast transitions) are fairly moderate for a lens in this class. The problem is most pronounced at f/4 with average CA pixel with just over 1px. The problem is almost negligible when stopping down to f/5.6 or beyond.

Verdict

The Canon EF 17-40mm f/4 USM L is a very good performer without a significant weakness. It's generally very sharp and contrasty across the image field. Vignetting is very well controlled - at least when using it on an APS-C DSLR. You may spot some barrel distortion when using the lens at 17mm but it's not all that bad. Typical for most wide-angle zooms chromatic aberrations can be visible but the problem remains comparatively low. The quality of the construction is next to perfect. Looking a bit beyond the APS-C scope it is worth to mention that the lens didn't perform quite as well during our corresponding full format test so the straight-forward idea of buying it now for an APS-C DSLR and using it at a later stage on a full format DSLR may not be as desirable as it may appear. It also faces stiff competition from the Canon EF-S 17-55mm f/2.8 USM IS which is both faster and slightly superior. However, from a price/performance perspective it is still an attractive lens for APS-C users.

Optical Quality:    
Mechanical Quality:
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